This invention relates generally to telephone lines, and more particularly, to qualifying telephone lines for data communications.
Public switched telephone networks, e.g., plain old telephone systems (POTS), were originally designed for voice communications having a limited frequency range. Today, the same POTS networks often carry data transmissions using higher frequencies. The difference in frequencies suggests that some POTS lines, which function well for voice, will function poorly for data. The risk of poor quality data transmissions has motivated telephone operating companies (TELCO's) to develop tests for predicting the quality of lines for data transmissions.
One quality test uses physical line length to determine a line's attenuation. The attenuation of a line whose length is less than about four kilometers (km) is usually low enough for data transmission. But, measuring the line length is typically more involved than measuring the straight line distance between a customer's address and a switching station. Typically, lines form branching structures rather than going radially from the switching station to the customer addresses. Thus, determining a line length usually entails manually mapping the actual branching structures connecting the customer to the switching station. Such complex manual techniques can be time intensive and may lead to errors.
Furthermore, determining that a line's length is less than a preselected limit, e.g., four km, may be insufficient to qualify the line for data transmission. The line's attenuation also depends on the physical properties of each branch segment making up the line, e.g., the gauge mixture of the line. In lines having segments with different properties, the above-described mapping technique generally should take into account the properties of each segment to determine the total attenuation of the line.
TELCO's have also used direct electrical tests to determine the quality of POTS lines for data transmissions. Typically, such tests are manual and two-ended. Two-ended tests involve sending one employee to a customer's address or final distribution point and another employee to a switching station. The two employees coordinate their activities to perform direct electrical measurements on the customer line using hand-held devices. These two ended measurements are substantially independent of the termination characteristics at the customer's address. An example of two-ended measurements is described in ROEHRKASTEN W: ‘MESSUNG VON XDSL-PARAMETERN’ NACHRICHTENTECNIK ELEKTRONIK, DE, VEB VERLAG TECHNIK. BERLIN, vol. 48, no. 2, 1 Mar. 1998 (1998-Mar.-01), pages 20–21, XP000752845 ISSN: 0323-4657.
Nevertheless, these two-ended tests need two separate employees, which makes them labour intensive. The labour requirements affect the cost of such tests. The two-ended tests cost about $150 per customer line. This cost is so high that a TELCO is often prohibited from using such tests for all customer lines.
HEDLUND, ERIC; CULLINAN, TOM: ‘DSL Loop Test’ TELEPHONY, vol. 235, no. 8, 24 Aug. 1998 (1998-Aug.-24), pages 48–52, XP002147002 USA, mentions single-ended testing but does not specify how such testing may be performed.
The present invention is directed to overcoming, or at least reducing, one or more of the problems set forth above.